All Standard C++ header files must be included in the following way:
#include //note: no ".h" extension#include//...other #include statements
That is, the “.h” extension should not be used. This technique applies to a subset of standard C header files as well, with the addition of the letter ‘c’ affixed to their name. So a C standard header formerly named
#include //formerly: mind the prefix 'c' and the omission of ".h"
The older convention for C headers,
#include using namespace std; //this is a using directivevoid f(){ printf ("Hello World
");}